The objective of this research is: a) to isolate cell lines that fail to process or degrade their RNA; b) to identify ribonucleases in the nucleous and cytoplasm of an established cell line; c) to allocate physiological functions to various ribonucleases; d) to find the function of poly (A) in messengers; e) to understand the process of heterogenous RNA turnover in the nucleus; and f) to comprehend the process of rRNA turnover. These objectives will be pursued by a combination of physiological, biochemical and genetical analyses. The processes of stable RNA and mRNA inactivation and degradation will be studied. For this purpose some established techniques and some new techniques will be used. In order to identify the ribonucleases and other enzymes, proteins from nucleus, and cytoplasm would be assayed in a variety of ways for the ability to synthesize poly (A) and the ability to degrade specifically unique polyribonucleotides such as a single-stranded, double-stranded and RNA in RNA-DNA hybrids. For this purpose a technique - namely chromatography of ribonucleases on single-stranded DNA agarose columns -would be employed. In order to isolate mutants in the various processes outlined, mutagenized cells will be grown in multiwell plates and labeled with radioisotopes, and mutants that would fail to degrade or synthesize specific RNA molecules under a defined set of conditions would be looked for by means of autoradiography. On the other hand, also mutants that fail in a specific ribonuclease function will be tested for by using the same multiwell plates. BIBLIOGRAPHIC REFERENCES: Apirion, D. The fate of mRNA and rRNA in Escherichia coli. Brookhaven Symp. on processing of RNA. Editor, J.J. Dunn. pp. 286-306 (1975). Kaplan, R., and Apirion, D. Decay of ribosomal RNA in Escherichia coli cells starved for various nutrients. J. Biol. Chem. 250: 3174-3178 (1975).